Since this now seems like the fermentation forum, I have another one. How does everyone out there measure their fermentation temperature accurately? I use one of the sticky thermometers on the side of the carboy as well as an indoor/outdoor thermometer, with the outdoor "probe" pressed against the side of the carboy and the indoor part (the actual base unit) a few feet away to measure ambient air temperature. Until this batch, I fermented in my basement or on the basement steps, depending on the temperature I needed (the top of the steps is about 70F and the basement floor is 64F in summer and in the upper 50s in winter).

My concern is that the outside of the carboy is not very accurate for measuring temperature. Is the sticky thermometer only taking the temperature of the glass touching it (which is presumably the temperature of the wort directly behind it) or is it influenced by the ambient air temperture (which should be cooler since the yeast activity in the wort is generating heat)? Do any of you use thermometers inside the fermenter? If so, how far down in the fermenter is the temperature being taken? I know a Ph.D. in microbiology and he said that in a fluid with yeast fermenting, there will be a difference in temperature at different depths within the liquid, possibly up to a few degrees.

I ask all of this since I am having a hard time keeping the fermentation temperature down in my Scotch Ale. With the high gravity, the yeast activity is strong and it is generating quite a bit of heat, too much to just let it sit on the basement floor. I fortunately just finished my freezer conversion, so I had it available for the fermenter. I set my fridge to 60F and verified the fridge temperature with my other thermometer, yet the carboy sticky thermometer read 65F, and I feared that the internal wort temperature may even be higher. I turned the temperature down to 58F and after a day and some slight slowing in yeast activity, the sticky thermometer reads 61F to 62F.

Yes, absolutely a vigorous ferment will raise the temperature of your beer above ambient temperature. That's why it is important to measure the beer temp and not air temp.

I use the same method of fixing a remote temperature probe to the carboy with great success. The only thing you have to do is insulate it from the air. I use some 1/2" foam around the probe, but really you could use anything that acts as an insulator.

And I don't like those sticky thermometers. They are hard to read precisely, and they aren't going to read beer temp unless you insulate them well, too, which defeats the purpose since you won't be able to see them to read the temp.

So if you are shooting for a target fermentation temperature, how much cooler do you have the ambient temperature at the start of fermentation? I figure the gap from ambient to wort temperature is greatest at the height of fermentation, say 12 to 36 hours after it kicks off and the gap decreases as fermentation slows.

Until recently, I have not had issues since I brewed beers at or below 1.060 and the gap at start up was about 2 degrees. I recently started making IPAs over 1.070 that had vigorous fermentations that raised my temperature too high (gap of 4 degrees ambient to wort) and I had overly fruity beer. Now I have a Scotch Ale and I am working hard to keep it cool enough. Just wondering if anyone had a rule of thumb based on SG as to how much of a gap in temperature to expect.

IMO the indoor outdoor, and even the stick ons are not going to be accurate enough for some styles, and would probably affect repeatability. The surface temp of the vessel is going to be a kind of average between the ambient and the centre of the ferment, since the ambient is "touching" the thermometer.
I drilled a hole in the top of my fermenter, made a well with a length of 1/2 inch copper pipe and a bulkhead fitting to isolate from the outside, and I drop probe into the well. That way I am measuring the centre of the ferment.
Cheers.

I copied a few ideas from this forum and covered a probe thermometer with tubing. I then placed it in the middle of my fermentation through the second hole in my carboy cap. I use a wort chiller cabinet. I studied the ambient temp outside, inside the chiller, and inside the ferment. I also had a sticky on the side. There was approximatly a 6 degree difference in my fermentation 36 post pitch from the chiller temp. I find that I have to set the chiller thermostat to 62F to get a 68 fermentation temp. Interesting enough, the sticky thermometer was inline with my probe inside the ferment. That was enough for me to trust it. I don't think fractions of a degree matter much as long as the beer-to-be is kept below 68 or so.

There was approximatly a 6 degree difference in my fermentation 36 post pitch from the chiller temp. I find that I have to set the chiller thermostat to 62F to get a 68 fermentation temp.

So if your chiller has a thermostat with a 4 degree differential, then the temp would cycle from 58F to 62F when set to 62F and the average ambient would be 60F, so wouldn't that be an 8 degree differenece to the wort? Or is your differential on the plus side of the set temp?

I use a thermowell probe with a Ranco controller. The probe is in the wort, and the controller can add heat via a Fermwrap wrapped around the carboy, or cool via the fridge that the carboy is sitting in.

Last year a bunch of us compared side temperatures to liquid temperatures & found no difference within the accuracy of our equipment (for mine 0.5F). I've also compared the temperature at various levels and did not see any stratification until the ferment was almost complete. Your biggest problem is that sticky, as mentioned.

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I use a thermowell probe with a Ranco controller. The probe is in the wort, and the controller can add heat via a Fermwrap wrapped around the carboy, or cool via the fridge that the carboy is sitting in.

This seems to be the optimal solution. Did you specially modify a vinyl blow cap to accommodate the probe? Can you post some pictures of your set-up? To me, if this can be done without risk of contamination this is the way to go. Your controller is actually controlling the temp of your beer throughout the fermentation process prior to secondary storage. I am getting ready to order two brewers edge controllers with the probe and heat package to control temp throughout the brewing process. I imagine the heater will rarely be needed in my neck of the woods.